1. Field of the Invention
The present invention relates in general to a pressure sensor housing, and more particularly to an apparatus that allows a pressure sensor in a sealed enclosure measure atmospheric pressure in a hostile environment. The present invention further relates to a pressure sensor system particularly suited for use in a tire pressure management system for generating a signal when a change in pressure in the tire exceeds or falls below a predetermined set point.
2. Description of the Related Art
There is a large percentage of vehicles being operated today with at least one tire underinflated or even overinflated. While some types of tires are somewhat tolerant to low pressure, the load capacity and life of any tire is related to inflation pressure. Heat generated within a tire from flexure can cause premature wear and in some cases sudden failure which may cause accidents or be catastrophic. While some tire companies have responded to this situation with "run-flat" or self-sealing tires, the loss of pressure within a tire still is somewhat undetectable and eventually if unnoticed the tire may fail. Thus, it is desirable to utilize tire pressure management systems. Tire pressure sensing on vehicles has several potential benefits, like safety and economy.
There are various types of pressure sensors known in the art, including tire pressure sensor systems.
U.S. Pat. No. 4,701,742, issued to Ruehr, describes a pneumatically operated pressure switch for monitoring the air pressure in a tire. The housing capsule of the pressure switch is designed so as to be mounted in a conventional rim of a motor vehicle wheel, or even mounted inside the wheel rim.
U.S. Pat. No. 4,793,277, issued to Haas, et al., also relates to a tire pressure detector for a motor vehicle which is designed to be fastened to a wheel rim.
U.S. Pat. No. 4,954,677, issued to Alberter, et al., describes a tire pressure sensor that is constructed to be fastened to a rim of a vehicle wheel and employs a referenced pressure chamber filled with a gas.
U.S. Pat. Nos. 4,890,090; 4,975,679; 5,055,826; and 5,119,066, all issued to Ballyns, relate to various pressure sensor systems for tires.
Gas permeable membranes have been known in the art, primarily to allow pressure equalization in vehicular electronics closures. This method of pressure equalization reduces the amount of ambient moisture condensation that is pumped into the enclosure. Manufacturers supply membrane materials like GORE-TEX.RTM. to electronic assembly producers such as Bosch, United Technologies, Seimens, and Caterpillar, among others. It is believed that Caterpillar has used a breather membrane to allow atmospheric pressure into the interior of their 3406 PEEC engine control to effect altitude compensation for their fueling algorithms.
There still exists a need for a tire pressure management system that allows atmospheric pressure to penetrate an environmentally sealed enclosure or housing to create an equilibrium which would allow a pressure sensor to achieve a proper reading even in a hostile environment and to make any necessary adjustments in pressure readings.